Removal of phosgene impurity from boron trichloride by laser radiation

ABSTRACT

Phosgene, COCl 2 , an impurity in BCl 3  is dissociated by CO 2  ser radiation that is passed through a stainless steel laser cell with NaCl windows on each end of the cell. The power level of a cw CO 2  multiline laser can be varied to accomplish the irradiation to effectively dissociate the COCl 2  into its dissociation products, substantially CO and Cl 2 . The BCl 3 , ν 3  (956 cm -1 ) fundamental is resonant with CO 2  (P 20 ) laser line and strongly absorbs this energy which is followed by an intramolecular V--V transfer of energy to the COCl 2  which results in its dissociation. The gaseous compound C 2  H 4  having combination bands and overtones that match reasonably close to the energy levels of COCl 2  can also serve as a diluent for COCl 2  to effect transfer of energy for dissociation of COCl 2  by cw CO 2  laser radiation.

DEDICATORY CLAUSE

The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to us of any royalties thereon.

BACKGROUND OF THE INVENTION

Commercially available BCl₃ (boron trichloride) of the highest purity still contains up to 0.1 percent COCl₂ (phosgene) contaminant. This contaminant or impurity causes difficulties when BCl₃ is used in the electronics industry, as a catalyst in numerous ways such as in the production of styrene, as an additive for high energy fuels, in the refining of various refractory metals, etc. Removal of the impurity from BCl₃ by economical methods has to data proven unsuccessful.

Advantageous would be a method to remove phosgene from boron trichloride or to change the phosgene to dissociation products which do not interfere with boron trichloride for its particular function or whereby the dissociation products of phosgene can be easily separated by conventional methods if required for boron trichloride catalysis function.

Therefore, an object of this invention is to provide a method for the dissociation of phosgene in the presence of BCl₃ without loss of BCl₃ concentration.

Another object of this invention is to provide a method to purify BCl₃ from the contaminant phosgene with laser radiation.

A further object of this invention is to provide a method for dissociation of phosgene in BCl₃ with a cw CO₂ laser radiation whereby the fundamentals of BCl₃ are resonant with the laser radiation to effect energy transfer to COCl₂ and results in its dissociation.

Still a further object of this invention is to provide a method of dissociation of phosgene in the presence of C₂ H₄ that has combination bands and overtones that match reasonably close to the fundamental energy of phosgene to effect efficient V--V transfer of laser energy responsible for the dissociation of phosgene.

SUMMARY OF THE INVENTION

The removal of COCl₂ impurity in BCl₃ is accomplished by using cw CO₂ laser radiation. Mixtures of BCl₃ and COCl₂ and mixtures of C₂ H₄ and COCl₂ are irradiated by cw CO₂ multiline laser at a power level to achieve dissociation of COCl₂. BCl₃ and C₂ H₄ are gaseous compounds which are involved in the energy transfer from laser radiation to COCl₂ to cause dissociation of the COCl₂.

The gases in admixture were metered into a stainless steel cell with NaCl windows on each end to achieve a predetermined pressure and subsequently exposed to cw CO₂ multiline laser radiation for a predetermined period of time to effect dissociation of COCl₂. The predetermined pressure is to ensure efficient irradiation by the power level of the laser employed. That is, the molecular concentration of the gas in the cell should be in consonance with the power level of the cw CO₂ multiline laser to achieve an efficient transfer of energy from the gases, either C₂ H₄ or BCl₃, to COCl₂ to effect dissociation of the COCl₂. The spectra of the static products are then obtained with a spectrophotometer (e.g., Beckman IR5) to evaluate the experiment to ascertain that the COCl₂ has been dissociated and to ascertain any depletion of the BCl₃ or C₂ Hhd 4 concentration.

BRIEF DESCRIPTION OF THE DRAWING

The figures of the drawing are infrared spectra wherein the percent transmittance is shown on the ordinate and the wave number and wavelength are shown on the abscissa.

FIG. 1 is the spectra of BCl₃ at 50 and 100 torr pressure showing the ν₄ (849 cm⁻¹) and ν₂ (1827 cm⁻¹) bands of COCl₂ impurity.

FIG. 2 is the spectra of the gases of FIG. 1 after being mixed with varying concentrations of H₂ and irradiated with cw CO₂ laser radiation.

FIG. 3 is the spectra of a mixture of 50 torr pressure BCl₃ and 0.8 torr pressure COCl₂ after being irradiated with a 100 watt cw CO₂ multiline laser.

FIGS. 4 and 5 are spectra which further illustrate the destruction of COCl₂ in BCl₃ without loss of BCl₃ concentration, using a CO₂ laser and a few seconds irradiation time.

FIG. 6 is the spectra of a mixture of 6 torr pressure of COCl₂ and 50 torr pressure of C₂ H₄. Curve b illustrates the destruction of COCl₂ but not as efficiently as when BCl₃ is used to transfer energy to COCl₂.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The BCl₃ was obtained from Matheson Gas Products and had a stated impurity of 0.1% COCl₂ maximum. It was used without further attempts to purify it. The H₂ (hydrogen) was obtained from Silox Inc., and used without further purification as were the COCl₂ and C₂ H₄ (ethylene) which were obtained from Matheson Gas Products.

The gases were metered into a laser cell (e.g., a 10 cm by 3 cm stainless steel cell with NaCl windows on each end) to provide a pressure in the range from about 5 torr to about 100 torr. Irradiation was accomplished with a cw CO₂ multiline laser at varying power levels. The unfocused beam was passed through the cell for a given period of time after which the spectra of the static products were obtained with a Beckman IR5 spectrophotometer.

The detailed description of the drawing includes the figure captions as related to the experimental procedures as follows:

Fig. 1. spectra of BCl₃ (with the COCl₂ contaminant).

a. 100 torr pressure.

b. 50 torr pressure.

Fig. 2. the spectrum of 25 torr pressure of BCl₃ (with the COCl₂ contaminant) and 25 torr pressure of H₂ before and after irradiation (O) for 2 sec with a 150 watt cw CO₂ laser. The term WDO ABS is window absorption.

Fig. 3. spectra of 50 torr pressure of BCl₃ and 0.8 torr pressure COCl₂.

a. Before irradiation.

b. After 3 sec irradiation time - 100 watts cw CO₂.

c. Additional 1 sec irradiation time - 100 watts cw CO₂.

Fig. 4. spectra of 6 torr pressure BCl₃ and 6 torr pressure COCl₂.

a. Before irradiation.

b. After irradiation with a 100 watt cw CO₂ laser for 15 sec.

Fig. 5. spectra of 10 torr pressure BCl₃ and 100 torr pressure COCl₂.

a. Before irradiation.

b. After irradiation with a 100 watt cw CO₂ laser for 15 sec.

c. After an additional 20 irradiation time.

Fig. 6. spectra of 50 torr pressure C₂ H₄ and 6 torr pressure COCl₂.

a. Before irradiation.

b. After irradiation with a 100 watt cw CO₂ laser for 50 sec.

The irradiations of mixtures of BCl₃ and COCl₂ were accomplished with varying power levels of a cw CO₂ multiline laser; however, the data illustrated by the Figures are based on a power level of a 100 watt cw CO₂ multiline laser except as in FIG. 2 where the power level was at 150 watts.

FIG. 3 is the spectra of 50 torr pressure BCl₃ and 0.8 torr pressure COCl₂. After 3 sec irradiation time most of the COCl₂ has disappeared (as evidenced by reference curve b) and an additional 1 sec irradiation essentially removes all the COCl₂ from BCl₃ without an appreciable depletion of the BCl₃ concentration. FIGS. 4 and 5 are spectra which further illustrate the destruction of COCl₂ in BCl₃ without loss of BCl₃ concentration, using a cw CO₂ multiline laser and a few seconds irradiation time as noted hereinabove.

FIG. 5 (b and c) shows the appearance of the CO band at 2143 cm⁻¹. Also, the addition of H₂ to the cell after the irradiation resulted in large amounts of HCl being formed which indicates that Cl₂ was present. The CO band and the formation of large quantities of HCl on addition of H₂ indicates quite convincingly that the dissociation products of COCl₂ are CO and Cl₂.

The BCl₃, ν₃ (956 cm⁻¹) fundamental is resonant with the CO₂ (P₂₀) laser line and strongly absorbs this energy. The laser induced chemistry (LIC) reaction BCl₃ + H₂ →HBCl₂ + HCl (See FIG. 2) is based upon this resonant absorption by ν₃ (BCl₃). COCl₂ does not have a fundamental resonant with the CO₂ laser, consequently when pure COCl₂ was irradiated, there was no change in the COCl₂ concentration. This indicates that the BCl₃ is involved in the dissociation of the COCl₂. Thus, it is proposed that the BCl₃ absorbs energy from the CO₂ laser radiation, which is followed by an intramolecular V--V transfer of energy to the COCl₂ which results in its dissociation into CO and Cl₂. The ν₃ (240 cm⁻¹) fundamental of COCl₂ and the ν₄ (243 cm⁻¹) fundamental of BCl₃ are sufficiently close for efficient V--V transfer of energy.

If indeed the above mechanism is responsible for the dissociation of COCl₂, then one could confirm this with another molecule having a fundamental that is resonant with the CO₂ laser radiation and with a fundamental whose energy is close to that of one of the COCl₂ fundamentals.

FIG. 6 shows 6 torr of COCl₂ mixed with 50 torr of C₂ H₄. The ν₁₀ (995 cm⁻¹) fundamental of C₂ H₄ is resonant with the CO₂ laser radiation and does absorb this energy. However, C₂ H₄ has no fundamentals very close to the energy of the COCl₂ fundamentals but there are combination bands and overtones that match reasonably close. FIG. 6 (b) illustrates that the COCl₂ is being removed but not as efficiently as in the case where BCl₃ is used for the transfer of energy.

The experimental data from this work strongly suggests that laser radiation can be used to purify materials that have fundamentals that are resonant with the laser radiation, BCl₃ being a case in point, wherein efficient V--V transfer of energy takes place between the material being purified (BCl₃) and the contaminant (COCl₂).

As shown by examples, the contaminant COCl₂ is dissociated by laser radiation if a diluent is employed such as C₂ H₄ which has combination bands and overtones that match reasonably close to the energy of the COCl₂ so that energy transfer takes place to effect dissociation. This technique of using a diluent could be advantageous if neat phosgene were desired to be dissociated as a means to dispose of the poisonous gas. This same technique may be applicable to other combinations of an undesirable and a diluent or a host material which contains a contaminant whereby the contaminant or undesirable compound can receive energy transfer from laser radiation via a gaseous diluent or host material to effect dissociation.

The disclosures of this invention indicate that the irradiation method could be adapted for continuous flow operation or for batch operations whereby the gaseous components in a container or cell are irradiated by laser energy to effect dissociation of the undesirable or contaminant compound.

Other diluent compounds or host compounds having fundamentals that are resonant with the laser radiation or having combination bands and overtones that match reasonably close to the energy of the COCl₂ could be selected for use with the method of this invention.

The primary object of this invention is to purify BCl₃ from COCl₂ contamination by laser irradiation to effect a dissociation of COCl₂. The invention method can be adjusted to use higher power laser irradiation for larger systems or as may be required for maximum energy utilization. If separation of the dissociation products are required for the end use of the BCl₃ then a separation step selected as modified from the prior art can be used in conjunction with this method. 

We claim:
 1. A method for dissociation of COCl₂ by laser irradiation of COCl₂ in presence of a gaseous compound selected from BCl₃ and C₂ H₄, said selected gaseous compound when BCl₃ having a fundamental whose energy is close to that of one of the COCl₂ fundamentals and said selected gaseous compound when C₂ H₄ having combination bands and overtones that match reasonably close to the energy of COCl₂ so that a transfer of energy takes place between said selected gaseous compounds and said COCl₂ when irradiated by laser radiation to effect dissociation of said COCl₂ when irradiated by laser radiation to effect dissociation of said COCl₂, said method comprising:i. metering said selected gaseous compound and said COCl₂ in admixture into a laser cell to achieve a predetermined pressure of said selected gaseous compound and said COCl₂ which comprise the gaseous components in said laser cell, said predetermined pressure to ensure consonance between the concentration of said gaseous components and the power level of a cw CO₂ multiline laser employed to irradiate said gaseous compound and said COCl₂ to effect dissociation of said COCl₂ ; ii. irradiating said selected gaseous compound and said COCl₂ in admixture by a cw CO₂ multiline laser at a predetermined power level of said cw CO₂ multiline laser for a predetermined time period to effect dissociation of said COCl₂ ; and, iii. obtaining a spectra of the static products of said admixture to detect said dissociation products of said COCl₂ and to determine when all the COCl₂ has been dissociated into dissociation products which are substantially CO and Cl₂ and said spectra to additionally detect any appreciable depletion of said selected gaseous compound.
 2. The method of claim 1 wherein said selected gaseous compound is BCl₃ and said COCl₂ is present as a contaminant in an amount of about 0.1%, said predetermined pressure is in the range from about 50 torr to about 100 torr; said predetermined power level of said cw CO₂ multiline laser is about 100 watts; said predetermined time of irradiating is from about 3 seconds to about 4 seconds; and wherein said spectra detects that essentially all of said COCl₂ has been dissociated into said dissociation products and that no appreciable depletion of said BCl₃ concentration has taken place.
 3. The method of claim 1 wherein said selected gaseous compound is C₂ H₄ and said COCl₂ are mixed to form said admixture wherein said predetermined pressure of said C₂ H₄ is about 50 torr; said predetermined pressure of said COCl₂ is about 6 torr; said predetermined power level of said cw CO₂ multiline laser is about 100 watts; and said predetermined time or irradiating is about 50 seconds.
 4. The method of claim 1 wherein said selected gaseous compound is BCl₃ and said COCl₂ are mixed to form said admixture wherein said predetermined pressure of said BCl₃ varies from about 6 torr to about 50 torr and said COCl₂ varies from about 0.8 torr to about 100 torr; said predetermined power level of said cw CO₂ multiline laser is about 100 watts; said predetermined time of irradiating is from about 4 seconds to about 35 seconds; and wherein said spectra detects that essentially all of said COCl₂ has been dissociated into said dissociation products and that no appreciable depletion of said BCl₃ concentration has taken place.
 5. The method of claim 4 wherein said predetermined pressure of said BCl₃ is about 50 torr, said predetermined pressure of said COCl₂ is about 0.8 torr; and said predetermined time of irradiating is about 4 seconds.
 6. The method of claim 4 wherein said predetermined pressure of said BCl₃ is about 6 torr; said predetermined pressure of said COCl₂ is about 6 torr; and said predetermined time of irradiating is about 15 seconds.
 7. The method of claim 4 wherein said predetermined pressure of said BCl₃ is about 10 torr; said predetermined pressure of said COCl₂ is about 100 torr; and said predetermined time of irradiating is about 35 seconds. 